ADD: javadoc for merge type

src/mhtree/MergeType.java

@@ -5,12 +5,18 @@ import messif.objects.LocalAbstractObject;
 import java.util.List;
 
 public enum MergeType {
+    /**
+     * Every object in descendants leaf node's bucket is retrieved and returned.
+     */
     OBJECT_BASED {
         @Override
         public List<LocalAbstractObject> getObjects(Node node) {
             return node.getObjects();
         }
     },
+    /**
+     * Returns the hull objects of {@code node}'s hull.
+     */
     HULL_BASED {
         @Override
         public List<LocalAbstractObject> getObjects(Node node) {
@@ -18,5 +24,12 @@ public enum MergeType {
         }
     };
 
+    /**
+     * Return a list of objects from the {@code node} specified by the merge type.
+     * Result is used for building a new hull.
+     *
+     * @param node a node
+     * @return a list of objects from the {@code node} specified by the merge type
+     */
     abstract public List<LocalAbstractObject> getObjects(Node node);
 }